The invention relates to photography and photographic methods and equipment and more particularly relates to a depressurized underwater one-time-use camera having a seal integrity indicator and related method.
Underwater cameras, by their nature, are sealed against entry of water during use. One-time-use underwater cameras are also usable unsubmerged. While used in air, protection from entry of rain, dust, or the like, may also be desirable. Since access is not required for film loading, a one-timeuse camera can be sealed air- and water-tightly during manufacture. This can be problematic if the one-time-use camera is left out in the sun. A sealed camera that is left out in the sun can develop a high internal pressure. This can cause damage to camera components. The water-tight seal may be lost, without any visible distortion of a housing or cover.
One solution to this problem is the use of a housing that can be repeatedly opened and closed. This is comparable to the use of a reusable camera with a housing or cover that is opened at least every time film is loaded or use of a separate underwater housing that is installed only for underwater use. The housing can be opened as necessary to prevent overpressurization. This solution is not desirable for one-time-use underwater cameras, which are intended for casual use without restrictive procedures.
Japanese patent publication JP 6-294992A, published Oct. 21, 1994, teaches a waterproof camera case that provides a valve that vents air (or other gas) to relieve excess internal pressure. The valve can also be used to evacuate air and add nitrogen at reduced pressure. This approach provides venting to reduce pressure, but adds one or more parts and some complexity. The valve also presents an additional risk of leakage.
U.S. Pat. No. 4,763,145 teaches a camera that adjusts internal air pressures to permit configuration changes such as moving a lens barrel between a wide-angle position and a telephoto position. Space within the camera for expansion and contraction is provided by a movable piston, elastomer member, or the like. A manual valve is optionally provided for venting.
U.S. Pat. No. 5,870,632 teaches a leakage detector which is used with a waterproof casing of a camera that is pressurized to greater than atmospheric pressure. The leak detector indicates if pressurization is decreased due to leakage.
Two shot injection molding is a well-known technique that provides one-piece plastic castings that are made of different materials in different regions of the casting. The different materials are united by codiffusion of adjoining regions of the two different materials. During molding, conditions are selected such that the molecules of the two different regions diffuse together before solidification. The codiffused zones have interpenetrating polymer networks. (This is also referred to as xe2x80x9cmolecular entanglementxe2x80x9d.)
A variety of two shot molding techniques are known, such as those disclosed in U.S. Pat. Nos. 6,066,282; 4,460,534; 6,296,796; and 5,737,002. Among these techniques is the use of a hard engineering plastic for one of the regions and a tougher, but softer material such as an elastomer, for another region of the casting. EP 0 865 779 A1 discloses an orifice coupling that has an internal, soft wiper seal formed by two shot injection molding. The use of two shot molding for the housing of an underwater one-time-use camera is disclosed in U.S. Pat. No. 5,832,312.
U.S. Pat. No. 4,999,664 teaches an exposure control that responds automatically to water pressure when submerged.
It would thus be desirable to provide improved camera and method in which an underwater camera remains fully and visibly sealed all during use.
The invention is defined by the claims. The invention, in broader aspects, provides a photography method, in which a partial vacuum is provided within a pressure housing of a camera having an unexposed film unit. The camera is sealed against both air entry and venting, while in the partial vacuum. The camera is kept sealed until the film unit is fully exposed and while sealed, a relative pressure differential between the interior of the camera and an environment external to the camera is continuous-indicated. The camera has a housing having an internal cavity water-tightly sealed from the external environment. The internal cavity has an unsubmerged internal pressure, at room temperature, less than air pressure at sea level. The camera has a camera frame assembly disposed in the internal cavity and a seal integrity indicator that provides the continuous indication of the relative pressure differential.
It is an advantageous effect of the invention that an improved camera and method are provided, in which an underwater camera remains fully and visibly sealed all during use.